Mesoscale Precipitation Discussion 0671
NWS Weather Prediction Center College Park MD
755 PM EDT Wed Aug 15 2018

Areas affected...Northwest AZ...Eastern CA...Southwest UT...NV

Concerning...Heavy rainfall...Flash flooding possible

Valid 152355Z - 160400Z

Summary...Heavy showers and thunderstorms will continue for few
more hours. Some additional flash flooding is possible.

Discussion...Late-day GOES-16 visible satellite imagery shows an
expansive area of shower and thunderstorm activity ongoing across
the broader region of the Southwest U.S., with some of the more
concentrated activity occurring over northwest AZ, far eastern CA,
central and southern NV and southwest UT. The convection has been
developing and evolving within an unstable boundary layer, with
MLCAPE values locally exceeding 1000 j/kg and in relatively close
proximity to a couple of MCVs.

The boundary layer has been rather dry and contributing to rather
large dewpoint depressions, but the relatively concentrated degree
of 500/700 mb layer moisture as denoted in the CIRA-LPW product is
helping the more organized and deeper convective cores to be more
efficient in generating heavier rainfall rates which have been
exceeding 1 inch/hr. The convection has been rather slow-moving
owing to weak mean-layer flow, and there has been the added
contribution of orographics in allowing some locally focused areas
of heavy rainfall.

Convection will continue to gradually exhaust the available
instability going through the evening hours, but there will
remains concerns for some additional flash flooding for a few more
hours. The more prone areas will remain the burn scar areas, dry
washes and local slot canyons.

Orrison

ATTN...WFO...FGZ...LKN...SLC...VEF...

ATTN...RFC...CBRFC...CNRFC...

LAT...LON   40761580 40541445 40061395 38731327 38351216
            37171175 35921188 34971270 34781353 35081427
            34681524 35101594 35671605 37101594 38101636
            38971693 40041682